My prediction is a rehash of D1. Dark Below style season (back to the moon or darkness arriving), House of Wolves style season (Uldren returning as a guardian, possible Queen Mara focus or Mithrax focus turning the wolves to light), Taken King style season (Savathun or the Darkness launching an assault of some sort), and top it off with a good ole Rise of Iron SIVA themed season.

I’m thinking the progression would be Darkness guardians coming out and a growing divide. The next season focuses on gathering allies to make up for the losses to the dark side. Basically if we can use the dark, why not ask for help from others? Then Savathun makes her arrival or the darkness arrives and things get significantly worse. Ending with Rasputin pushing back the darkness with SIVA but turning on the guardians that chose darkness to preserve humanity, light users take it as an act of aggression and Rasputin becomes an enemy, eventually being corrupted himself.